1. Technical Field
Embodiments of the present invention relate to an image forming apparatus, a controller, and a method of forming a multicolor toner image.
2. Related Art
In a known image forming apparatus, a full-color toner image is formed by superimposing toner images of multiple component colors on an image bear and transferring the superimposed toner images from the image bear onto a recording sheet in a transfer unit. At that time, relative misalignment of one or more of the toner images of the multiple component colors is generally either corrected or reduced.
That is, for example, multiple linear patch images are formed and transferred onto a secondary transfer roller, which generally holds and conveys the recording sheet in a prescribed direction as a recording sheet conveyor, and multiple positions of the linear patch images are detected on the secondary transfer roller. The known image forming apparatus then corrects relative misalignment of one or more of the multicolor toner image based on a result of detection of the respective positions of multiple linear patch images. That is, in the known image forming apparatus, the patch images are formed on multiple photoconductive drums for respective component colors and are transferred onto an intermediate transfer belt in respective primary transfer nips formed therebetween, in which the multiple photoconductive drums and the intermediate transfer belt press against each other. Then, the patch images of respective component colors transferred onto the intermediate transfer belt are secondarily transferred onto a circumferential surface of the secondary transfer roller in a secondary transfer nip formed therebetween as a secondary transfer station, in which the intermediate transfer belt and the secondary transfer roller press against each other. Here, a secondary transfer condition, such as a secondary transfer voltage, a secondary transfer current, etc., under which a secondary transfer process is executed in the secondary transfer nip, is conventionally equalized to a transfer condition under which a full-color toner image obtained by superimposing toner images of multiple component colors (hereafter simply referred to as a full-color toner image) is secondarily transferred. Subsequently, an optical reflection type sensor detects the multiple patch images of respective component colors borne on the secondary transfer roller.
Since the reflection type sensor generally includes a light emitting element and a light receiving element, a light beam emitted from the light emitting element is reflected by a surface of the secondary transfer roller and reaches the light receiving element ultimately. When the respective edges of the patch images formed and borne on the secondary transfer roller are detected, an amount of light received by the light receiving element changes. Specifically, the reflection type sensor outputs a detection signal having a rising portion and/or a falling portion in a prescribed waveform thereof in accordance with the amount of light received by the light receiving element. The outputted detection signal is then compared with a prescribed threshold, and prescribed pulses are outputted as patch image detected time indicating pulses in accordance with comparison result for the multiple component colors. A position of each of the patch images of the respective component colors is detected (i.e., identified) based on a time when the reflection type sensor detects and outputs the patch image detected time indicating pulse. Based on a result of such positional detection of each of the patch images of the respective component colors, an image forming condition, such as an exposing time, a driving speed profile, etc., is corrected (i.e., adjusted) to reduce relative misalignment of one or more toner images of component color or colors in the multiple component color toner image when it occurs.